There is an increasing demand for higher quality, higher resolution and higher definition in the recognition or evaluation of color of an object to be measured (hereinafter, also, referred to as DUT), such as displays, cosmetics, printed matters, paints and other objects that are evaluated or perceived in terms of colors, and hence the measurement of the color sense of a DUT is now becoming more and more important. Here, by the term "color sense", in this description, is intended the feel or impression of the quality (attribute, property, nature, quality of a material, etc.) of a DUT by the human visual perception of color, gloss (or glaze), texture and pattern of the DUT. However, there has not yet been developed up to now a color sense measuring device for measuring the hue, saturation and lightness of a DUT and determining or evaluating synthetically or totally the color sense that a person perceives through his eyes from the DUT surface with high accuracy on the basis of the results of measurements of the DUT.
In general, the color of a DUT is measured by obtaining a spectral distribution of the DUT using a spectrophotometer. The spectrophotometer comprises an optical section and a measuring section. The optical section is constructed by a spectroscope for generating monochromatic light and a part for measuring the intensity of reflected light. The measuring section performs calculation processing of measured signals.
The results measured by the spectrophotometer are displayed, for example, as a graph showing the relationship between the wavelength and the intensity of light represented on the abscissa and ordinate, respectively. This graphic representation is commonly referred to as a spectral distribution.
The color of a material can be represented or displayed usually in terms of three attributes of the material, i.e., hue, lightness and saturation. The relationships between these attributes and the spectral distribution can be known by examining the spectral distributions of hue difference, lightness difference and saturation difference using a color chart and a spectrophotometer.
A visual comparing method or a mixed color matching method is a visual inspection method for comparing a specimen with a systematized color scale by the visual sense to measure and evaluate the color of the specimen.
A stimulus direct-reading method and spectrocolorimetric method are a method for measuring a color by use of a calorimetric instrument manufactured in conformity to the requirements stipulated in JIS (Japanese Industrial Standard) Z 8722 (Method for Measuring Colors of Objects) or the like.
The spectrocolorimetric method is a method for measuring the spectral reflectance or spectral transmittance of the color of a DUT, performing a calculation processing by a prescribed method, and determining a systematized coordinates in space of the color (as to the above, refer to "Measurements of Colors" published by Society of Input Standards (Nyuryoku Kikaku Kyokai)).
The above-mentioned visual comparing method and the mixed color matching method are a method for evaluating the color of an object by visual inspection, and hence they are required to eliminate a defect that the evaluation varies with individual operators or inspectors and/or measuring environments.
The stimulus direct-reading method and spectrocolorimetric method are a method for performing a photoelectric colorimetry using a photoelectric tube unlike the visual colorimetry, and hence it is possible to measure or evaluate colors with relatively high accuracy because they do not rely upon the naked eye. However, it is required to perform measurements or evaluations of colors with higher accuracy and measurements or evaluations of colors in the absolute value with higher accuracy. That is, the stimulus direct-reading method, which is capable of reading tristimulus values from a meter using a photoelectric colorimeter, evaluates the color of a specimen (DUT) by reading tristimulus values of both of a sample and the specimen. On the other hand, the spectrometric method can perform measurements of colors with high accuracy as well as measurements of colors in the absolute values with high accuracy. However, these methods have a problem in the measurement of dark colors (as to the above, refer to page 94 of "Common Sense of Colors" published by Society of Japanese Standards (Nippon Kikaku kyokai)).
Further, in the visual colorimetry, it is necessary to prevent the results of measurements from being influenced by surface conditions of a sample and a DUT, the size of the DUT, the arrangement of the sample and the DUT, and other conditions for the measurements. It is also necessary to avoid that the surface condition of the DUT is affected and changed by its temperature and humidity so that a measurement error is caused.
Heretofore, it is intended that the color of a DUT is measured by such methods as mentioned above and the measured results are properly processed to measure or determine the color sense of the DUT. However, it is impossible to obtain the results of colorimetry of the DUT with high accuracy.